Invisible waterproof printing fluid



UNITED sTArEs- PATENT OFFICE.

HERBERT P. PEARSON, OF NEW YORK, N. Y., ASSIGNOR TO KENDALL PRODUCTS I CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

INVISIBLE WATERPROOF PRINTING FLUID.

110 Drawing.

To all whom it may concern:

Be it known that I, HERBERT P. PEARSON, a subject of the United Kingdom of Great Britain, residing in the United States, in the city of New York, county of New York, and State of New York, have invented certain new and useful Improvements in Invisible lVaterproof Printing Fluids, of which the followin is a specification.

This invention re ates to the formation of invisible waterproof characters on paper, textiles or other material. Such characters retain their invisibility until the paper or other material on which they are impressed is moistened with water or aqueous solution. During this operation, the water-repellent characters prevent the wetting of the portions of the material which they cover, so that because of the difference in the lightabsorption properties of the dry and wet portions of the material,, the characters be come visible.

It is a primary object of the present invention to provide a printing medium having a comparatively slow rate of evaporation and therefore being suitable for use'on a press, so that the marking of the characters'need not be done by hand, but may be accomplished by the ordinary process of printing.

The invention accordingly proposes to employ for the printing medium a substantially colorless water-repellent wax or other suitable substance dissolved in or mixed with a liquid having a rate of evaporation approximating that of water. The waterrepellent substance is preferably a wax or wax-like material, such as paraffin and the like, and the liquid is preferably a solvent for the said material having a moderate rate of evaporation, such as tetrachlorethane or xylol, or a mixture thereof.

' It will be readily understood that the ingredients of the printing medium and their proportions may be varied through wide limits, and that the invention is not restricted to any specific ingredients or pro portions'thereof, except as specified by the claims. As an example of the ingredients and the proportion in which they may advantageously be employed, it may be noted that excellentresults may be obtained by the use of about five per cent. by weight of paraflin dissolved in ninety-five per cent. by

I Specification of Letters Patent.

Application filed September 12, 1921.

Patented Dec. 27, 1921.

Serial No. 500,154.

material, thus relying on the equality of the 1 colors for rendering the characters invisible.

The printing medium proposed by the present invention. may be used on an ordinary printing press because of its moderate rate of evaporation. A solvent of high volatility, such as alcohol, cannot be so employed because it evaporates before reaching the paper or other material, having to be transferred thereto by way of the inking rollers and the printing surface. Wood cuts are preferably employed for delivering the printing medium to the paper, as these cuts absorb some of the liquid and become uniformly moistened therewith, thus producing an even print. After having thus been applied to the paper or other material, the

liquid evaporates and leaves fine particlesof the water-repellent substance, deposited on the fibers of the material, thus rendering the same resistant to water at the parts where the said medium is applied. Owing to its colorlessness this deposit is invisible.

When the paper thus printed is moistened,

however, the water or other aqueous liquid is absorbed only by the unimpregnated portions of the paper, so that the print is at once rendered visible. When the paper dries the characters disappear. As long as the water-repellent substance remains on the material, the characters may be rendered "isible repeatedly by renewal of the moistening operation. -They may removed, when desired, by treating the paperor other material with any suitable solvent for the water-repellent substance, such as carbontetrachlorid, alcohol or the like.

Having thus described my invention, what I claim is:

1. As a medium for printing invisible water-repellent characters, a solution of a water-repellent substance, invisible relawater-repellent characters, a mixture of a substantially five per cent. solution of paraiiin in a mixture of xylol and tetrachlorethane in substantially equal parts.

5. A medium for printing invisible water-proof characters, consisting of an agent having a rate of evaporation approximating that of water, and forming an invisible water-repellent deposit on the material to which it is applied.

In testimony whereof I have allixed Ill) signature to this specifi -ation.

HERBERT P. 1 E All SON. 

